The c-raf-1 protooncogene is altered in several human malignancies. Research on Raf-1 has focused on its activation during cell cycle entry following cellular stimulation with mitogens. In preliminary studies I have found that the c-Raf-1 kinase is hyperphosphorylated and activated in mouse fibroblasts arrested in mitosis, suggesting that Raf-1 may play a role in the G2/M transition of the cell cycle as well. The following series of experiments are proposed: (1) Mapping and mutagenesis of the sites of mitotic Raf hyperphosphorylation (2) Identification of upstream effectors of Raf-I phosphorylation and activation (3) Characterization of downstream targets of activated Raf-I in mitosis.